Aromatic hydrocarbons, which are common environmental pollutants, may be metabolized aerobically through the initial activation of the aromatic ring initiated by the insertion of oxygen atoms by monooxygenase or dioxygenase enzymes from bacteria [9, 24]. Such aerobic biotransformations may result in the production of intermediates that contain epoxide or dihydrodiol functional groups that may be then further metabolized. It is well known that heme-type cytochrome P450 generally produce aromatic epoxides that may be further metabolized to trans-dihydrodiols [3, 25] while non-heme bacterial dioxygenases produce cis-dihydrodiols from aromatic ring structures (FIG. 1) [28, 32].
Recently, the present inventors reported flavanone epoxide formation by the biphenyl dioxygenase (BDO) of Pseudomonas pseudoalcaligenes strain KF707 (SEQ ID NO:3) after expression in Escherichia coli, and this unique monooxygenase activity was explained based on the structural properties of the flavanone in the active site [10]. In this case, the flavanone B-ring was unable to form the biphenyl-type structure required for dihydrodiol formation due to the position of the C-3 tetrahedral center on the flavanone structure and may be compared to previous studies where flavanone substrates that possessed the same B-ring conformation as biphenyl were biotransformed to flavone cis-dihydrodiol by biphenyl dioxygenase [20, 27].
Flavonoids are a large group of natural products that have recently been garnering much attention in the disciplines of nutrition, food science, environmental science, and pharmacology due to their potential beneficial effects on health [19]. Actually, flavonoids exhibit inhibitory effect on capillary permeability, peripheral circulation improving effect, anti-inflammatory effect, anti-atherogenic effect, antioxidant effect, anti-allergic effect, and anti-cancer effect, and thus have potential uses as medicine [2, 12, 15, 34]. For example, isoflavones, such as genistein (4′,5,7-trihydroxyisoflavone) and daidzein (4′,7-dihydroxyisoflavone), are natural edible phytoestrogens found mainly in leguminous plants, and due to their structure similar to a mammalian estrogen [13, 17, 35], they appear to play an important role in preventing hormone-dependent diseases such as breast cancer, prostate cancer, and osteoporosis [1, 11, 14, 18].
The study of BDO biotransformation of flavonoids may aid in the production of new biologically active compounds as well as provide mechanistic insights into the functioning of BDO. The present inventors reported the absolute configurations of four isoflavan-4-ol stereoisomers in the previous study [36].
Throughout the entire specification, many papers and patent documents are referenced and their citations are represented. The disclosures of cited papers and patent documents are entirely incorporated by reference into the present specification, and the level of the technical field within which the present invention falls and details of the present invention are explained more clearly.